African trypanosomes have evolved a highly complex mechanism for camouflaging themselves from the immune defenses of their mammalian hosts. This phenomena is manifested through their seemingly endless repertoire of antigenically distinct but homogeneous surface glycoproteins (Variant Specific Surface Antigens, VSSAs or VSGs). The potential for VSG expression fluctuates during the trypanosome life cycle which consists of several morphologically distinct differentiated forms. We have prepared a cloned complementary DNA (cDNA) sequence for one specific VSSA from T. brucei. Southern blot hybridization analyses of restriction enzyme digestions performed with our cloned VSSA cDNA probe on the genomes of two T. brucei clones expressing different VSSA genes have demonstrated that their active and inactive gene states are contextually different. We would like to analyze this phenomenon in detail to determine whether somatic recombination or gene mobility are in part responsible for VSSA gene expression and potentially the VSSA diversity. Recombinant DNA techniques will be employed to: (a) prepare cDNA clones for other temporally related VSSA mRNAs, (b) assess the nucleotide sequence homologies of antigenically distinct as well as isotypically related VSSA, (c) determine the overall organization of VSSA genes, (d) analyze the extent of the VSSA gene repertoire, (e) ascertain the potential role of DNA recombination in VSSA repertoire expansion, (f) determine whether RNA processing and splicing of VSSA nuclear transcripts are in part responsible for the regulation of VSSA gene expression, (g) to determine whether the expression of other, possibly less abundant trypanosome gene products are trypanosome class specific and whether these exhibit coordinate or non-coordinate expression with VSG's.